The present invention relates to a technique to improve sound through addition processing of a plurality of sound signals.
Recently, most of sound reproducing devices for stereophonically reproducing music or the like have compact housings for improving the portability and the space saving property. In a compact sound reproducing device, a distance between two speakers for an L-channel and an R-channel is so small that differences in time and level between sounds output from the two speakers and reaching respective ears of a person are small, and hence, expansion of a resultant sound field is poor.
As a conventional countermeasure, an acoustic processing technique for improving the expansion of a sound field by adding, to a signal of a given channel, an anti-phase component (an indirect path component) of a signal of the opposite channel before outputting a resultant sound from a speaker has been disclosed (see, for example, JP-A-10-028097).
In sound signals of music or the like to be reproduced by a sound reproducing device, sound of vocals or the like is included in sound signals of the L-channel and R-channel as in-phase components so that its sound image may be localized in the center in stereophonic reproduction. However, when an anti-phase component of a sound signal of the R-channel (or the L-channel) is added to a sound signal of the L-channel (or the R-channel) on the opposite side, the in-phase components included in the sound signals of the L-channel and the R-channel interfere with each other to be degraded, resulting in causing a problem that the density of a sound image obtained in the center is lowered. For example, when music is reproduced with a conventional stereophonic reproducing device, although a sound field is expanded in the lateral direction, vocal sounds localized in the center may be sometimes difficult to be heard.